1. Field of the Inventions
The present application generally relates to the field of prosthodontics and more particularly to a method and apparatus for planning a dental component.
2. Description of the Related Art
A tooth supported artificial dental prosthetic, such as a crown or bridge, can cover portions of a tooth surface and is normally fabricated away from the patient's mouth, in a lab, and then installed in the mouth by the dental practitioner. A tooth preparation, as used herein, is a tooth that has been reshaped for accepting dental prosthetics. To achieve a strong fitting of a dental prosthetic, it is important for the surface of the tooth preparation to coincide closely with the mating surface of the dental prosthetic.
Typically, for a dental crown, after diagnosing that a patient needs a dental prosthetic, the dentist grinds down the tooth to be reconstructed and takes two impressions and a wax bite of the patient's jaws. Based on the impressions, a technician prepares a corresponding cast. The prepared cast typically comprises two parts corresponding to the upper and lower jaw. One of the parts includes a representation of the preparation. The representation of the preparation is referred to as a die; which is a physical representation of the preparation. The die is often sectioned from the overall cast of the jaw so that it can be individually viewed and manipulated.
A finish line (also known as “preparation line”) is defined as the apical limit of the preparation and the margin of the prosthetic typically ends on it. After the prepared cast of the patient's dentition is created, the finish line can be manually marked by the lab technician in ink on the die. An insertion line is the direction of insertion of the prosthetic onto the preparation. The insertion line is chosen, in part, so as to avoid collisions with adjacent teeth. The finish line and path of insertion line are important parameters used in constructing and implanting the crown or bridge.
In recent years, dental prosthetic design has been accomplished increasingly using computer systems and 3D computer graphics or CAD (computer-aided design) software. These systems allow a dentist, dental technician, or other operator to design dental prosthetics for individual patients. These individual prosthetic designs are often called “situations,” “dental plans,” or “prosthetic plans.” The prosthetic plans that are made in the 3D or CAD software are typically based on the scans of the patient's teeth, gums, and bone structure and other system constraints. Once the dentist has loaded all of the relevant data for the patient, the plan can be refined. A virtual three-dimensional (3D) image of the cast is obtained e.g. in a manner as described in international publication No. WO97/03622, or in international publication No. WO00/08415.
U.S. Pat. No. 5,417,572 discloses a computer-based method for extracting a finish line for designing an artificial crown. Amounts of variation of data representing the shape of a preparation are determined, and a train of points is extracted from the amounts of variation. The finish line for designing the artificial crown is determined, based on thus displayed train of points. U.S. Pat. No. 7,488,174 discloses a computer-based method for constructing a crown to be fitted on a preparation in a subject. The method comprises defining a finish line to obtain finish line data and employing the finish line data in constructing the crown. The finish line is determined by providing a three-dimensional digital data relating to the patient's dentition and generating first finish line data which is updated with second finish line data obtained from a dental practitioner.
As noted above, the finish line is an important design constraint for the final prosthetic. An accurate finish line enables optimal mating between the preparation and the crown. Thus, the more precisely the 3D or CAD model reproduces the anatomy of the mouth in the areas to be treated, the more accurate will be the spatial position as will be the static and dynamic relationships within the mouth after treatment.
Even with these advanced 3D or CAD software systems, a physical model of the patient's jaw and the preparation is typically needed. The physical model is used to check the fit between the crown (which can be designed on the 3D or CAD software system) and the preparation. In addition, the interaction between the crown and the adjacent jaw can be checked. U.S. Pat. No. 7,220,124 discloses a method of machining a physical model based upon a 3D computer graphics or CAD representation of the impressions of the patient. By machining the physical model, certain improvements in accuracy can be achieved as compared to traditional plaster cast based models which are cast directly from the impressions of the patient jaw. In a similar manner, U.S. Pat. No. 7,384,266 also discloses a method of machining a physical model from 3D computer graphics or CAD representation of the impressions of the patient. In this case, the physical model can be divided up into more than one part. For example, the model can be segmented into individual tooth components.
While the above described 3D or CAD software systems and methods of creating a physical model are useful, in practice, they can be cumbersome for a dental practitioner to use. For example, they often require the practitioner to make multiple decisions and require several individual steps in order to create the desired physical model. In a similar, manner 3D or CAD software systems require multiple steps to create a prosthetic. There also remains a need to eliminate the cast physical model while still maintaining dimensional accuracy, particularly in prosthetic applications which place a higher demand on accuracy than other applications such as orthodontic applications.